A court in Belarus jailed a U.S. lawyer for three years on Monday on charges of industrial espionage and carrying forged documents, a verdict certain to plunge relations between the two countries deeper into crisis.

The trial of New York-based lawyer Emmanuel Zeltser, a specialist in Russian law and organized crime, was held behind closed doors. The verdict was announced by the defendant's lawyer, Dmitry Goryachko.

"My position is that he did not commit these crimes," Goryachko told Reuters. "We will, of course, be making an appeal."

Zeltser's secretary, Vladlena Bruskova, was jailed for a year.

The U.S. State Department has repeatedly expressed concern over his arrest and sought his release on grounds of ill health.

On Monday, the U.S. embassy said it could not judge whether the trial met international standards as it had not been present. It repeated calls to be granted access to Zeltser.

"We have not been granted consular access to him for more than two months," it said. "We ... call upon the Belarsussian authorities to provide him with all the medication which has been prescribed to him."

Zeltser was detained in March on his arrival in Belarus, where he was to represent the interests of Josef Kay, a relative of the late Georgian businessman Badri Patarkatsishvili.